Segmental precast concrete post-tensioned overpass bridges with cantilevered abutment

ABSTRACT

A bridge structure particularly adapted for construction in skewed orientation with respect to a lower, overpassed roadway comprises a bridge portion, end abutments, and an intermediate support column. The bridge portion is constructed by supporting a plurality of precast concrete open-topped box-beams and precast L-shaped parapet-sidewalk members on temporary falsework at the bridge site. Upstanding from the precast box beams are wooden flanges which are trimmed in place to provide temporary supports of desired heights for precast slabs forming a bed for the upper roadway. The variable-height supports are used to form a crown in the roadbed, or to form an inclined roadbed which may be part of a banked curve. The precast box-beams are joined together by formed-in-place concrete diaphragms which are poured simultaneously with a concrete roadbed, whereby a monolithic squared off bridge portion is formed. An intermediate support column engages one of the diaphragms, thereby eliminating an exposed transverse support beam. The bridge portion is post tensioned by means of longitudinal and transverse post tensioned tendons. The squared-off bridge portion extends between two abutments, and any skew angle between the upper and lower roadways is accommodated in the abutments by a diagonal rake or relief &#39;&#39;&#39;&#39;chamfer&#39;&#39;&#39;&#39; of the abutment corner closest to the roadway. The far side of the squared off end of the bridge portion engages the top of the unraked portion of the abutment wall at an expansion joint, and is supported thereon; the remainder of the end of the squared off bridge portion being supported in cantilever manner, projecting beyond the diagonally raked corner of the abutment. The diagonally raked portion of the base wall of the abutment is substantially parallel to the lower roadway, thereby providing adequate horizontal clearance therefrom. The top of the abutment provides the approach roadway for the bridge. The top of the abutment is supported on and integral with the base walls of the abutment, with a portion cantilevered outward beyond the raked portion of the base wall to meet the squared off bridge portion.

United States Patent [191 Schupack SEGMENTAL PRECAST CONCRETEPOST-TENSIONED OVERPASS BRIDGES WITH CANTILEVERED ABUTMENT MorrisSchupack, c/o Schupack Associates, 2701 Summer St., South Norwalk, Conn.06905 [22] Filed: July 8, 1971 [21] Appl. No.: 160,707

[76] Inventor:

[58] Field of Search 52/128, 174, 365, 79, 323, 52/227, 731, 223 R, 87,335, 338; 14/17, 73, 75; 249/1; 94/1 A [56] References Cited UNITEDSTATES PATENTS 3,566,557 3/1971 Comolli 52/335 X 2,602,321 7/1952 Blair14/75 X 3,367,074 2/1968 Vamich 52/174 X 3,570,207 3/1971 Launary....52/227 X 2,686,421 8/1954 Barron... 52/174 X 3,022,759 2/1962 McCall52/223 R X 3,300,921 1/1967 Middendorf 52/227 3,253,288 5/1966 Nagin14/73 3,295,276 l/l967 Rene 52/223 R X 3,555,753 1/1971 Magadini 52/2273,302,348 2/1967 Pratt 52/223 R 731,595 6/1903 Mueser 52/174 FOREIGNPATENTS OR APPLICATIONS 1,279,303 4/1968 Germany 52/227 29,140 l/l909Sweden 14/75 428,826 5/1967 Switzerland 14/16 OTHER PUBLICATIONSEngineering News Record, Box Members Distinguish Concrete Bridge, page86, June 27, 1946 Primary Examiner-Henry C. Sutherland AssistantExaminerCarl D. Friedman Attorney, Agent, or FirmMattern, Ware and Davis[57] ABSTRACT A bridge structure particularly adapted for construc- 1Feb. 26, 1974 tion in skewed orientation with respect to a lower,overpassed roadway comprises a bridge portion, end abutments, and anintermediate support column. The bridge portion is constructed bysupporting a plurality of precast concrete open-topped box-beams andprecast L-shaped parapet-sidewalk members on temporary falsework at thebridge site. Upstanding from the precast box beams are wooden flangeswhich are trimmed in place to provide temporary supports of desiredheights for precast slabs forming a bed for the upper roadway. Thevariable-height supports are used to form a crown in the roadbed, or toform an inclined roadbed which may be part of a banked curve. Theprecast box-beams are joined together by formed-inplace concretediaphragms which are poured simultaneously with a concrete roadbed,whereby a monolithic squared off bridge portion is formed. Anintermediate support column engages one of the diaphragms, therebyeliminating an exposed transverse support beam. The bridge portion ispost tensioned by means of longitudinal and transverse post tensionedtendons.

The squared-off bridge portion extends between two abutments, and anyskew angle between the upper and lower roadways is accommodated in theabutments by a diagonal rake or relief chamfer of the abutment cornerclosest to the roadway. The far side of the squared off end of thebridge portion engages the top of the unraked portion of the abutmentwall at an expansion joint, and is supported thereon; the remainder ofthe end of the squared off bridge portion being supported in cantilevermanner, projecting beyond the diagonally raked corner of the abutment.The diagonally raked portion of the base wall of the abutment issubstantially parallel to the lower roadway, thereby providing adequatehorizontal clearance therefrom. The top of the abutment provides theapproach roadway for the bridge. The top of the abutment is supported onand integral with the base walls of the abutment, with a portioncantilevered outward beyond the raked portion of the base wall to meetthe squared off bridge portion.

4 Claims, 12 Drawing Figures PAIENIEnrmemm' SHEETIBFY MATTERN WARE ANDDAVlS v ATTORNEYS mdE SnEEI s or 7 Pmmmmzsmm FIG. ll

PAIENIEUrmzsmu I sum 7 or 7 SEGMENTAL PRECAST CONCRETE POST-TENSIONEDOVERPASS BRIDGES WITH CANTILEVERED ABUTMENT SUMMARY OF THE INVENTIONThis invention relates to bridge structures, and more particularly tooverpass bridge structures fabricated of modular members, said bridgestructure also being easily oriented at any desired skew angle withrespect to a lower, overpassed roadway.

BACKGROUND OF THE INVENTION The massive limited-access interstatehighway program has necessitated the construction of thousands ofoverpass bridges, and many more thousands will be built in the nearfuture. Generally, these bridges have been constructed by one of twomethods. Both methods involve a substantial amount of custom designingand fabrication for each bridge, taking into account such factors as theskew angle of the upper roadway relative to the lower roadway, thelength of the span, horizontal and vertical curves in the upper roadway,and the super-elevation transition to be accommodated by the bridge.

The first general method of constructing such a bridge comprises formingan abutment at each end of the bridge span, and constructing the bridgespan of large steel beams supported at intermediate points by exposedtransverse beams and associated columns. A bridge deck is thenfabricated on the steel beams. If the bridge is skewed with respect tothe lower roadway, a correspondingly skewed expansion joint is necessaryat the ends of the bridge. A bridge of this type is expensive tofabricate, consumes a long construction time at the site, and requiresregular maintenance.

The second general mehod of constructing overpass bridges comprisesforming the bridge of cast-in-place concrete. This method requires onsite construction of elaborate custom forms, which are generally usedonly once. The forms are custom-designed to provide for horizontal andvertical curves in the bridge deck, and the like. It appears at thistime that the price of cast-inplace concrete has risen dramatically inthe past several years because of the price of such form work. Thismethod also requires extended on-site construction time with associateddisruption of normal traffic flow.

It was therefore desirable that a unified scheme for constructing aplurality of overpass bridges be achieved. This was particularlyimportant as several bridges located in one general area are oftenconstructed by a single builder. It was recognized that the use ofstandardized uniform precast materials could result in substantial costreductions and short construction times for such bridges.

OBJECTS OF THE INVENTION Accordingly it is a principal object of thepresent invention to provide a unified scheme for constructing bridges.

It is another object of the invention to provide a unitied schemeincorporating precast, modular members for constructing bridges.

It is an additional object of the invention to provide a unified schemefor economically constructing overpass bridges in skewed orientationwith respect to a lower overpassed roadway.

It is a further object of the invention to provide an overpass bridge inskewed orientation with the lower overpassed roadway wherein the bridgeabutment supports the squared off end of the bridge span and alsoprovides adequate horizontal clearance from the lower overpassedroadway.

It is yet another object of the invention to provide an overpass bridgein skewed orientation with the lower roadway wherein the expansion jointfor the bridge is not skewed, but extends transversely, perpendicular tothe upper roadway.

A still further object of the invention is to provide a unified schemefor constructing overpass bridges wherein variations in theconfiguration of the bridge deck of a particular bridge are readilyaccommodated.

An additional object of the invention is to provide for constructingbridges with uniform minimum bridge deck thickness.

It is another object of the invention to provide an overpass bridgepartially supported by an intermediate pier wherein no exposedtransverse support beam is necessary.

It is yet another object of the invention to provide an attractive andsafe overpass bridge.

It is an additional object of the invention to reduce the cost andconstruction time of overpass bridges.

Other and more specific objects will be apparent from the features,elements, combinations and operating procedures disclosed in thefollowing detailed description and shown in the drawings.

THE DRAWINGS FIG. 1 is a fragmentary perspective view of an overpassbridge according to the invention, viewed from below;

FIG. 2 is a top perspective view of a precast opentopped box-beam usedin constructing the bridge of FIG. 1;

FIG. 3 is a top perspective view of a precast slab used in constructingthe bridge of FIG. 1;

FIG. 4 is a top perspective view of a precast sidewalkparapet memberused in constructing the bridge of FIG. 1;

FIG. 5 is a top exploded perspective view of the abutment of theoverpass bridge of FIG. 1;

FIG. 6 is a side elevation view of the overpass bridge of FIG. 1;partially constructed;

FIG. 7 is a top plan view, partially cut away of the overpass bridge ofFIG. 1;

FIG. 7A is a top plan view of the skewed expansion joint of a prior artoverpass bridge;

FIG. 8 is a cross-sectional view of the over-pass bridge of FIG. 1 takenalong the line 88 of FIG. 7;

FIG. 9 is a fragmentary cross-sectional view partially broken away ofthe overpass bridge of FIG. 1 taken along the line 99 of FIG. 7;

FIG. 10 is an enlarged fragmentary view of the crosssection of theoverpass bridge shown in FIG. 8; and,

FIG. 11 is a longitudinal, elevation sectional view, partially broken,of the overpass bridge taken along the line 11-11 of FIG. 7.

The same reference characters refer to the same elements throughout theseveral views of the drawings.

GENERAL DESCRIPTION The unified scheme for constructing overpass bridgesaccording to this invention includes a squared-off elongated-rectangularmonolithic bridge span constructed primarily of modular precastrectangular members. The basic precast modular members comprise precastopen-topped box-beams incorporating longitudinal hollow tubes forreceiving tensioning tendons; precast slabs for forming the top of theboxbeams and for spanning the spaces between spacedapart rows ofbox-beams to form the bottom portion of the bridge deck and to supplythe positive reinforcing steel therefore, and precast L-shapedsidewalk-parapet members. All of the precast modular members includesteel reinforcing rods, portions of which protrude for appropriateengagement linking the members.

The open-topped box-beams and sidewalk-parapet members are supported ontemporary falsework at the bridge site. Temporary bridge slab formsupports com prising wooden boards protruding upward from the box-beamsare cut to proper elevation to support the precast slabs at accurateheights to assure the desired configuration of the bridge deck. Formsare placed to define transverse intermediate and end diaphragms joiningthe box beams, and the forms also include provisions for an intermediatesupport pier engaging one of the intermediate diaphragms in longcontinuous span bridges. Concrete is placed in situ to form the bridgedeck and the diaphragms, linking the precast members into a monolithicbridge span. The bridge span is posttensioned by transverse andlongitudinal tendon cables to supply the primary support.

The unified scheme also includes attention to abutments foraccommodating the squared-off bridge span in bridges having a skewedorientation with respect to the lower roadway. The abutments comprisevertical walls and an integral cap. A first portion of the verticalabutment wall positioned transverse to the upper roadway engaginglysupports over one-half of one end of the bridge span, and the remainderof the end of the bridge span protrudes outwardly being supported incantilevered manner. A second portion of the vertical wall of theabutment is diagonally raked at an angle to the first portion, whereinthe second portion is substantially parallel to the lower roadway toprovide adequate horizontal clearance therefrom. The top of the abutmentforms the approach to the bridge, and a portion of the top iscantilevered outward over the diagonally raked portion of the verticalabutment wall to meet the remainder of the squared-off end of the bridgespan. An expansion joint is provided along the squared off end of thebridge span, whereby the expansion joint is as short and consequently aseconomical as possible.

SPECIFIC DESCRIPTION Referring now to FIG. 1, there is shown inperspective a portion of an overpass bridge according to the invention.The bridge overpasses a divided lower highway, and the bridge is skewedwith respect to that lower highway. The bridge 10 generally comprises abridge span 12 and an abutment 14.

The bridge span 12 is constructed primarily of precast modular members.These members include three rows of open-topped box-beams 20, precastslabs 22 which cover the open tops of the box-beams and span thedistance between adjacent rows of box-beams, and L-shapedsidewalk-parapet members 24. The bridge span further comprisesintermediate diaphragms 26 and heavier end diaphragms 28 joining theprecast modular members into a unitary, squared-off bridge span.

The abutment 14 is custom-designed to adapt the squared-off bridge span12 to various orientations skewed with respect to the lower, overpassedhighway by means of a diagonal rake of the abutment corner closest tothe lower roadway. The abutment l4 accordingly comprises a first unrakedportion 30 of its vertical base wall, portion 30 being positionedtransverse to the upper roadway and engagingly supporting more thanone-half of the length of end diaphragm 28 and the associated bridgespan 12. Expansion bearings 74 permits movement between the bridge span12 and the abutment wall 30 to accommodate expansion and contraction ofthe bridge span caused by temperature changes. The remaining portion ofend diaphragm 28 protrudes outward toward the overpassed roadway and issupported in a cantilevered manner. A second portion 32 of the verticalabutment wall is diagonally raked away from end diaphragm 28, and ispreferably substantially parallel to the skewed lower roadway, providingample horizontal clearance therefrom (See FIG. 7). The remainingportions 31 and 33 of the vertical abutment wall extend parallel to theupper roadway to form the sides of the abutment.

An abutment top slab 34 with a cantilevered portion 36 forms theapproach to the bridge. The triangular cantilevered portion 36 of thetop slab extends outward beyond the diagonally raked portion 32 of thevertical abutment wall to meet the squared-off bridge span and completethe upper roadway. The abutment further comprises sidewalk-parapetmembers 38 cantilevered outward from the abutment cap 34. An expansionspace 40 adjacent to expansion bearings 74 remains between the bridgespan 12 and the abutment cap 34 to accommodate dimensional changes dueto temperature variation. (See also FIG. 11).

PRECAST MEMBERS One of the precast open-topped box-beams 20 is shownisolated from the bridge span in FIG. 2. It comprises a bottom plate 42,end webs 44, and side webs 46. Wooden boards 48 upstanding from the topof the box-beam 20 by a distance of several inches to one foot, alongthe inside of end webs 44 and flanking each of the side webs 46. Thewooden boards 48 are secured to the box beams by bolts 47, and flangesof greater height can be easily substituted if necessary for theparticular application. These flanges are cut to desired heights at theconstruction site, using a portable power saw for example, adapting themto support the precast slabs 22 in positions and altitudes correspondingto the desired configuration of the bridge deck surface.

The box-beam 20 further includes steel reinforcing rods for addedstrength. The steel reinforcing rods preferably protrude from thebox-beam for engagement with adjacent steel reinforcing rods protrudingfrom the other precast members, and for engaging with the cast in situconcrete intermediate and end diaphragms 26 and 28. The steelreinforcing rod stirrups 52 preferably terminate in loops protrudingalong the tops of end webs 44 and side webs 46, and preferably terminatein longitudinal protrusions 54 from the ends of box-beam The box-beam 20also has formed therein several elongated longitudinal tubes 56 forreceiving longitudinal post tensioning tendon cables. The positioning ofthese tendon tubes may be varied in the plurality of box-beams, so thatthe openings at the end of each boxbeam are aligned with the openings inthe end of the adjacent box-beam to form generally sinusoidal conduitsextending the entire length of the bridge span 12, the conduits inelevation resembling the catenary sag of suspension bridge cables, withhigh points at the ends of the bridge span and at the intermediatesupport columns, and with low points strengthening the lower fibers ofthe bridge for tension loading at the centers of the unsupported portionof the span. This configuration of post tensioning cables is well knownin the art. However, this well known method of positioning posttensioning tendons has the disadvantage of necessitating the non-uniformpositioning of tubes in each box-beam such that the overall assemblycomprises sinusoidal tubes. In addition to the individual specializedplacement of the tube form in each precast member, it is required thateach member be preplanned for its particular position in the bridgespan, labeled to indicate that position, and placed in that position atthe bridge site.

The disadvantages noted above are overcome in bridges constructed ofprecast segments as disclosed herein by utilizing a new configurationfor the post tensioning tendon cables. Referring now to FIG. 6, in thisconfiguration the cables are also high at the end abutments and at theintermediate support columns, and low adjacent to the centers of theunsupported portion of the span. However, the transition between thehigh and low portions of the tendon occurs entirely in the box-beams aand 20c positioned adjacent to the abutments and adjacent to the centersupport column 84. The tendon tubes now run in a straight line along thelower edge of the remaining box-beams 208. Thus only three differenttypes of box-beams are required. Box-beams 20a have tubes in parabolictransition between the low tendon position and a high, tendon anchorageposition. Box-beams 20c have a generally half sine wave tubeconfiguration providing transition upward from the low tendon positionand to a high tendon position, and providing a smooth transition acrosscentral diaphragm 26a. Both box-beams 20a and 200 are reversible. Thistube configuration greatly simplifies the procedure in precasting thebox-beams, and also greatly simplifies organization of the boxbeams atthe bridge site.

In addition to the great ease of construction achieved by thisconfiguration of the tendon cables, it has also been found that thisconfiguration gives greater structural strength than the well-knownsinusoidal configuration.

The open-topped box-beams 20, including the upstanding wooden boards 48,the internal reinforcing steel, and the longitudinal tubes 56, may bereadily and inexpensively fabricated in a concrete yard, and transportedto the bridge site on trucks. An elongated U- shaped steel form may beused to form the outside of the precast box-beams with a smooth, evenfinished appearance. Movable end plates within the U-shaped steel formpermit easy adjustment for forming boxbeams of various lengths, and a'wooden or steel form may be positioned in the form to form thehollowed-out center portion of the box-beams. The tension cable tubesand steel are then placed, and subsequently the concrete forming thebox-beams is placed in the form. Different web heights are achieved byusing adjustable height inside forms to permit filling the forms to adesired level. Casting of the box-beams can also be easily accomplishedat the bridge site if so desired, and size limitations caused bytrucking capabilities are thereby avoided.

Referring now to FIG. 3, there is shown a precast slab 22 used inconstructing the bridge span 12. The slab 22 has internal reinforcingsteel rods serving as the positive bridge deck reinforcing steel, whichprotrude as shown at 58 for engaging with the reinforcing steel of thebox-beam 20 and for engaging with concrete subsequently placed over andaround the slabs. The slab 22 is generally rectangular, havingdimensions such that it can be positioned with its peripheral edgesresting on the inboard wooden boards 48 upstanding from the box-beam 20,and wherein steel reinforcing rods 58 protruding from the edge of theprecast slab engage the loops of stirrups 52 upstanding from the webs ofboxbeam 20. Slabs 22 having longitudinal dimensions of over 20 feet aresomewhat flexible, and readily conform to the cut edges of the woodenboards even if they do not lie precisely in the same plane. Precast slab22 may have a slight crown, as indicated at 60, whereby the slab isstrengthened in its central, unsupported portions. A plurality of slabs22 are used in constructing the bridge span 12, some of which cover thetops of box-beams 20, and some of which span the distance between thethree rows of box-beams as can be seen in FIGS. 1, 7 and 8, therebycomprising the bottom portion of the bridge deck.

Using a precast slab containing positive reinforcing steel as the lowerportion of the bridge deck greatly reduces the possibility of the bridgedeck surface cracking. When the lower positive reinforcing steel and theupper negative reinforcing steel are placed and the entire bridge deckformed in situ, there has been a tendency for pockets to develop alongthe underside of the negative reinforcing steel. These pockets developbecause of settlement of the materials in the concrete mix away from thelower side of the negative reinforcing steel. When the bridge is in use,very fine cracks develop extending downward from the bridge deck surfaceto the negative reinforcing steel. Water and road salt seeping down thecracks collect in the pockets under the negative steel, and freezing ofthe water can cause the bridge deck surface to become pitted andextensively cracked, requiring expensive repairs.

By forming the lower portion of the bridge deck of precast slabs, a muchthinner portion of the bridge deck remains to be cast-in-place. Thesettlement problem is minimized in a thinner cast-in-place portion, andconsequently pockets below the negative reinforcing steel do not form.Without these pockets, the bridge deck is far less susceptible topitting and cracking. The result is a higher quality bridge deckrequiring minimum maintenance.

The third precast member utilized in constructing the bridge span 12 isthe L-shaped sidewalk-parapet member 24, shown isolated from the bridgespan in FIG. 4. The sidewalk-parapet member preferably has alongitudinal dimension approximately equal to that of boxbeam 20. Thesidewalk portion 62 is relatively thin, wherein utility conduits 86 (SeeFIG. 10) for telephone and electric lines and the like may be positionedthereon. As described below, additional later-placed concrete 87 is castover the sidewalk portion 62, encasing the utility conduits and furtherstrengthening and anchoring the sidewalk-parapet 24 firmly in itscantilevered position. The parapet, or guardrail portion 64 has thethickness desired for the final bridge structure.

The L-shaped sidewalk-parapet member 24 further comprises steelreinforcing rods, portions of which protrude for engagement withadjacent steel reinforcing rods and the later placed concrete. The steelreinforcing rods include longitudinal reinforcing rods which do notprotrude, and transverse reinforcing rods protruding at 68. The steelreinforcing rods also comprise L- shaped protrusions 70, which areanchored in the parapet portion 64, and which are later enclosed in theconcrete 87 placed over the sidewalk portion 62 to aid in securing thesidewalk parapet member into the bridge span in cantilevered manner.FIG. 10 shows a typical internal configuration of the steel reinforcingrods.

All of the above described members are preferably precast in a concreteyard, and transported to the bridge site on heavy equipment. Cranes,trucks and other equipment capable of handling precast members weighingup to 60 tons are readily available. Box-beams and sidewalk parapetmember 24 having lengths of 40 to 50 feet are'within this 60 ton limit.

ABUTMENT WALLS The first step in constructing the bridge is to constructtransverse portion 30 of the vertical abutment walls. The remainingportions of the vertical abutment walls may also be constructed at thistime; however, construction of the abutment cap may be deferred toprovide clearance for jacks used in post-tensioning until the bridgespan is completed. Referring now to FIG. 5, a perspective view of thevertical abutment walls is shown. They comprise the transverse portion30 which is relatively thick for engagingly supporting the transverseend diaphragm 28 of the bridge span 12. The second diagonally rakedportion 32 of the vertical abutment wall is disposed at an angle to thefirst portion 30, portion 32 being substantially parallel to the lowerdivided highway 72. A large clearance width W is thereby providedbetween the vertical abutment wall and first roadway 72a of the dividedhighway 72. (See FIG. 7). Such horizontal clearance would not beprovided if transverse portion 30 of the vertical abutment wall wereextended to the full width of the abutment. The vertical abutment wallsfurther comprise rearward extending walls 31 and 33.

Similar vertical abutment walls are constructed for the other end ofbridge span 12, the second abutment being appropriately reversed as canbe seen in FIG. 7, to provide adequate horizontal clearance W from thesecond roadway 72b comprising the lower divided highway.

The expansion bearings 74 are positioned on the top of transverseportion 30 of the vertical abutment wall. Referring now to FIG. 11, theexpansion bearing 74 comprises a lower steel plate 76 engaged with thetop of transverse portion 30 of the vertical abutment wall. Theexpansion bearing 74 further comprises an upper steel plate 78, and anelastomer material 80 which may be compressed rubber, positioned betweenthe two steel plates permitting sliding movement therebetween. Suchexpansion bearings are commercially available and are well known in theart.

CONSTRUCTION OF THE BRIDGE SPAN In the embodiment of the bridgedisclosed herein, the span comprises three parallel, spaced-apart rowsof box-beams 20, each row comprising eight box-beams having theiradjacent end faces aligned and spaced apart to accommodate intermediatediaphragms. Wider spans can be constructed using additional rows ofbox-beams, and narrower spans may comprise as few as one row ofbox-beams.

Upon completion of the vertical abutment walls and installation of theexpansion bearings as described above, construction of the bridge span12 is begun by supporting the box beams 20 in the three rows ontemporary falsework 82. (See FIG. 6). The temporary falsework compriseswooden or steel pier structures and each can be used to support theadjacent ends of two box-beams and the forms for the diaphragms. Twotemporary falsework piers are provided flanking the location of thecenter support pier 84, wherein clearance for forming this pier isprovided.

It is very important that the thickness of the bridge deck be uniform,as any unnecessarily thick portions can result in substantial amounts ofextra weight. Therefore, crown or twist variations in the configurationof the bridge deck are primarily accommodated in positioning thebox-beams. Referring now to FIG. 8, the bridge deck shown has a crownfor the purposes of drainage. The central row of box-beams is elevatedon the temporary falsework with respect to the outside rows by adistance approximating the desired crown. If it were desired to form abanked bridge deck, one of the outside rows of box-beams would besupported at a greater relative height.

Referring now to FIGS. 8 and 10, the wooden boards 48a and 48L along theoutside edge of bridge span 12 are cut to the height desired forengaging and supporting lower peripheral edges of sidewalk-parapetmembers 24. The sidewalk-parapet members are then temporarily supportedin the cantilevered manner shown by additional temporary falsework, notshown, extending upward from falsework 82.

The next step in constructing the bridge span 12 comprises positioningthe precast slabs 22 to form the bottom portion of the bridge roadbed.This is accomplished by first cutting the wooden boards 48b-k upstandingfrom the box-beams to desired heights for engagingly supporting theperipheral edges of the slabs 22. The height or grade to which theboards 48b-k are cut is also determined by the desired configuration ofthe bridge deck, and by the necessity of maintaining a uniform bridgedeck thickness. In the crowned bridge deck shown, board 48c is cut at aslightly greater height than board 48b to tilt precast slab 22a inaccordance with the crown, thereby providing fine adjustment of thebridge deck thickness.

As mentioned above, precast slabs having longitudinal dimensions of 20feet or more are somewhat flexible, and therefore the wooden boards maybe cut to define complex surfaces having more than one radius ofcurvature, and the precast slabs position on the boards will conformthereto. The wooden flanges 48 also compensate for minor irregularitiesin the positioning of the box-beams 20. This is accomplished by cuttingthe flanges in accordance with measurements obtained by means of a levelor other surveying equipment, rather than measuring upward from theprecast box-beam.

Vertical curves in the bridge deck are accommodated in a similar manner.The precast box-beams are raised near the high point of the curve, andthe wooden boards are cut to support the precast slabs in positionsaccurately defining the vertical curve.

The precast slabs can be eliminated from the bridge structure, and thebridge deck cast entirely in situ. The wooden boards 48 are also usefulwhen this method of construction is chosen. The wooden boards are cut tothe proper heights defining the bottom of the bridge deck, and metaljoist hangers are then attached to the boards to support joists on whichplywood form boards are supported covering the tops of the box-beams andspanning the space between the rows of box-beams. The reinforcing steeland the concrete for the bridge deck are then placed. After the concretehas hardened, the joists, joist hangers, form boards, and temporarywooden boards 48 are removed where visible to present an uncluttered,attractive underside of the bridge span. Utilizing the wooden boards totemporarily support such forms is much simpler than prior art methods ofsupporting such forms.

In the bridge disclosed herein five rows of precast slabs are positionedon the box-beams. Referring now to FIG. 7, the first row of precastslabs 22a covers the top of the first row of box-beams, the second rowof precast slabs 22b spans the open space between the first and secondrow of open topped box-beams, the third row of precast slabs 22c coversthe tops of the central row of box-beams, and the like.

As described above, the precast box-beams are supported on temporaryfalsework 82 with a space remaining between their facing end webs 44.This space accommodates any minor variations in the length of theprecast box-beams, and also accommodates the protruding steelreinforcing rods 54. The sidewalk-parapet members 24 are approximatelythe same length as the box-beams 20, and an open space 66 remainsbetween adjoining sidewalk-parapet members when they are positioned onthe temporary falsework.

The next step in constructing the bridge is to place forms for the enddiaphragms 28, the intermediate diaphragms 26, and for the centralsupport pier 84. The forms for the intermediate diaphragms 26 primarilybridge the space between the positioned box-beams, and the forms for theend diaphragms 28 are merely a box enclosure partially supported onabutment wall 30 and partially supported by falsework. The space .66between the sidewalk-parapet members is left open. Consequently, thesediaphragm forms are relatively simple, and represent a small amount oflabor and time.

The form for the central pier 84 is merely a vertical tube or elongatedbox upstanding from a footing 83, and opening into the form for thecentral intermediate diaphragm 26a, which is preferably somewhat widerthan the other intermediate diaphragms.

The upstanding wooden boards 48 supporting the slabs 22 also act ashaunch forms, preventing any concrete poured on the slabs from fillingthe box-beams or escaping through the bottom of the bridge span.

Utility conduits 86 are placed above the sidewalk portion 62 of thesidewalk parapet member 24, as is best seen in FIG. 10. The conduits 56are joined and secured between adjacent box-beams to avoid infiltrationof concrete and provide a complete through conduit for the longitudinalpost tensioning tendons. Additional steel reinforcing rods may be placedabove the precast slabs. Granite sidewalk curbs 88 may be positioned ifdesired, as can also be seen in FIG. 10, or forms for sidewalk curbs maybe placed. Conduits with tendons 45 for transverse post tensioning areplaced at the central intermediate diaphragms 26a, and end diaphragms28, as can be seen in FIG. 9.

After the elements described above have been positioned in the bridgespan l2, concrete is placed to form the support pier 84, theintermediate diaphragms 26, the end diaphragms 28, a roadbed surface 89,and the sidewalk 87. The concrete flows under the edges of the precastslabs up to the wooden boards to provide permanent support of the bridgedeck, the wooden boards thereby acting as haunch forms. The concretelinks all of the precast members and other elements of the bridge spaninto a single, unitary, monolithic structure.

When the concrete has hardened, the longitudinal tensioning cables 55are pulled through conduits 56. Hydraulic jacks are used to tension thetendons, and the tendons are held in tensioned condition by anchorages97 which are then preferably grouted (See FIG. 11). Referring now toFIG. 9, anchorages 47 holding transverse tendons 45 in tension conditionare shown at the central diaphragm 26a, the transverse tensioningtendons for the end diaphragms 28 being similar. The order of tensioningthese cables is determined for each particular bridge.

The bridge span 12 may be given an attractive finished appearance byadding raised concrete portions 17 at the ends of the intermediatediaphragms 26, as can be seen in FIG. 1, and a screen fence 19 or railmay be provided above the parapet portion 64 of the sidewalk parapetmember 24, as can be seen in FIG. 6. The exposed wooden boards may alsobe removed, as the temporary support they provided is no longernecessary.

ABUTMENT CAP The abutment cap 34 is now formed above the vertical basewalls of the abutment. Referring now to FIG. 5, the space 37 surroundedby the vertical abutment walls is filled with suitable fill material,and forms for the abutment cap 34 are placed. The cap 34 is shownexploded upward in FIG. 5, but is actually formed directly on top of andintegral with the abutment walls. Appropriate steel reinforcing rods arelaid in the form, and appropriate extra steel reinforcement 92 is placedin the area of the triangular cantilevered portion 36. The amount andpositioning of the reinforcing steel in the abutment cap is chosen totune the cantilevered portion of the cap with the cantilevered portionof the end of the bridge span. These two portions are tuned if theyremain aligned with each other throughout varying load and temperatureconditions. This is necessary in order that a bump does not exist at thetransition between the abutment cap and the bridge deck. Additionalsidewalk parapet members 38 are placed along the vertical abutmentsidewalls 31 and 33 (See FIG. 1), additional sections of utilityconduits 86 are laid along the sidewalk portions, and curb members areplaced. Concrete is then placed in the forms to comprise the abutmentcap; including the cantilevered triangular portion 36 thereof, and thesidewalks lying therealong.

Referring now to FIG. 11, an expansion space 40 is left between the enddiaphragm 28 and the abutment cap 34, this space accommodating expansion.of the bridge span 12. A suitable expansion joint 92 is placed to spanthe gap 40 and provide a smooth transition between the abutment cap andthe bridge span 12. A final road upper surface 95 of asphalt may be laidon the surface of the bridge span and on the abutment cap.

The expansion joint 92 is an expensive portion of the bridge, oftencosting more than a hundred dollars per linear foot. Referring now toFIG. 7, in the bridge disclosed herein the expansion joint 92 of lengthLjoining the squared off end of the bridge span and the abutment istransverse to the bridge span, and consequently as short as possible. Inprior art bridges wherein the end of the bridge span is skewed and mateswith a correspondingly skewed abutment, as is shown in FIG. 7A, a muchlonger expansion joint 92A of Length L is required. The substantialsavings achieved in the short expansion joint of the bridge disclosedmore than offsets the expense of cantilevering a portion of the abutmentcap.

The modular bridge span disclosed herein may also be used withsubstantial cost reductions in bridges which are not skewed with respectto the lower roadway. In such a bridge, the abutment wall 30 may extendthe width of the bridge span, supporting the end diaphragm 28 along itsentire length thereon. Thus, no cantilevered portions of either thebridge span or the abutment cap are necessary.

Substantial savings realized in constructing bridges according to thescheme disclosed herein also stem from a reduction of on-siteconstruction time and labor costs. Bridge members which are precastgenerally cost less than formed-in-place concrete, primarily because ofthe extensive on-site formwork required in the latter method. By placingall of the positive reinforcing steel for the bridge deck in theprecast-slabs, the need for specialized workers to lay such steel at thebridge site is minimized. Savings in architectural and bridge designerfees are also achieved, in that the unified scheme may be easilymodified to construct bridges of varying width and length.

Bridges constructed according to this scheme also have aesthetic andsafety advantages. Using a transverse support beam integral with thebridge deck, a center column is permitted which gives-the bridge a greatfeeling of airiness and minimizes the tunnel effect of a protrudingskewed support beam. The aesthetics of a single pier column supporting a-foot wide bridge is striking, and also affords extra visibility andconsequent safety. The wide box members and the large cantileveredsidewalk parapet members which shadow the outside box-beam minimizes themassiveness of the elevation view, and results in an extremelyattractive appearance.

Since the foregoing description and drawings are merely illustrative,the scope of the invention has been broadly stated herein and it shouldbe liberally interpreted to secure the benefit of all equivalents towhich the invention is fairly entitled.

I claim:

1. A bridge for skewed orientation with respect to a lower overpassedroadway or the like comprising A. a rectangular bridge span havingtransverse ends perpendicular to its longitudinal axis and having .1.longitudinal beams longitudinally spaced supporting a bridge deck,

2. transverse diaphragms connecting longitudinally spaced pairs of saidlongitudinal beams 3. transverse end diaphragms supporting terminal onesof said longitudinal beams and each forming a perpendicular transverseend of said bridge span and incorporating end anchorage means forreceiving post-tensioning tendons of the bridge span, accomodatingtendon cable ends for convenient non-skewed post tensioning,

B. an abutment for supporting the end of the rectangular bridge span andhaving l. a first support wall transverse to the bridge span axis andengagingly supporting a major portion of the transverse end diaphragm ofthe bridgespan, said first support wall having a first end adjacent to afirst bridge span corner furthest removed from the lower roadway, and asecond end positioned between the longitudinal axis of the bridge spanand the adjacent bridge span corner closest to the lower roadway,

C. a second wall positioned substantially parallel to the lower roadwayand extending diagonally from said second end of the first support wallto a point adjacent to the outside edge of the upper roadway; and

D. a cantilevered abutment slab supported by the second wall and havinga portion thereof cantilevered outward from said second wall injuxtaposed relation with the transverse end diaphragm of the bridge spanextending beyond said first support wall in cantilever fashion to forman approach to the bridge span.

2. An abutment as defined in claim 1 and further comprising:

D. expansion bearings positioned between the first support wall and thetransverse end diaphragm of the bridge span supported thereon permittingmovement of the bridgespan relative to the abutment.

3. A bridge span as defined in claim 2 and further comprising:

B. an expansion joint joining the transverse end diaphragm of the bridgespan and the abutment slab adjacent thereto, said expansionjoint'thereby lying transverse to the bridge span and consequently beingof minimum length.

4. An abutment as defined in claim 1 wherein the cantilevered portion ofthe abutment slab is provided with reinforcing steel dimensioned andpositioned to provide load deformation characteristics substantiallymatching those of the adjacent transverse end of the bridge span,whereby theslab is designed for load deformation movement correspondingto similar movement of the cantilevered portion of the bridge span undervarying load conditions.

1. A bridge for skewed orientation with respect to a lower overpassedroadway or the like comprising A. a rectangular bridge span havingtransverse ends perpendicular to its longitudinal axis and having 1.longitudinal beams longitudInally spaced supporting a bridge deck, 2.transverse diaphragms connecting longitudinally spaced pairs of saidlongitudinal beams
 3. transverse end diaphragms supporting terminal onesof said longitudinal beams and each forming a perpendicular transverseend of said bridge span and incorporating end anchorage means forreceiving post-tensioning tendons of the bridge span, accomodatingtendon cable ends for convenient non-skewed post tensioning, B. anabutment for supporting the end of the rectangular bridge span andhaving
 1. a first support wall transverse to the bridge span axis andengagingly supporting a major portion of the transverse end diaphragm ofthe bridge span, said first support wall having a first end adjacent toa first bridge span corner furthest removed from the lower roadway, anda second end positioned between the longitudinal axis of the bridge spanand the adjacent bridge span corner closest to the lower roadway, C. asecond wall positioned substantially parallel to the lower roadway andextending diagonally from said second end of the first support wall to apoint adjacent to the outside edge of the upper roadway; and D. acantilevered abutment slab supported by the second wall and having aportion thereof cantilevered outward from said second wall in juxtaposedrelation with the transverse end diaphragm of the bridge span extendingbeyond said first support wall in cantilever fashion to form an approachto the bridge span.
 2. transverse diaphragms connecting longitudinallyspaced pairs of said longitudinal beams
 2. An abutment as defined inclaim 1 and further comprising: D. expansion bearings positioned betweenthe first support wall and the transverse end diaphragm of the bridgespan supported thereon permitting movement of the bridgespan relative tothe abutment.
 3. transverse end diaphragms supporting terminal ones ofsaid longitudinal beams and each forming a perpendicular transverse endof said bridge span and incorporating end anchorage means for receivingpost-tensioning tendons of the bridge span, accomodating tendon cableends for convenient non-skewed post tensioning, B. an abutment forsupporting the end of the rectangular bridge span and having
 3. A bridgespan as defined in claim 2 and further comprising: E. an expansion jointjoining the transverse end diaphragm of the bridge span and the abutmentslab adjacent thereto, said expansion joint thereby lying transverse tothe bridge span and consequently being of minimum length.
 4. An abutmentas defined in claim 1 wherein the cantilevered portion of the abutmentslab is provided with reinforcing steel dimensioned and positioned toprovide load deformation characteristics substantially matching those ofthe adjacent transverse end of the bridge span, whereby the slab isdesigned for load deformation movement corresponding to similar movementof the cantilevered portion of the bridge span under varying loadconditions.